Which sites actively fight bots? (eg. use CAPTCHA s)? Just Pokerstars?

[Traveller99]

I would like to bias my play towards poker sites that actively fight bots. I think it would make sense if the sites would force players to occasionally enter a CAPTCHA (see http://en.wikipedia.org/wiki/Captcha). I’m not sure if any sites do this normally yet for all players (I doubt it), but I came across a post, which I found interesting as it suggests that Pokerstars does this (maybe with some criteria to trigger the CAPTCHA ?, or is it random intervals for all players ?)

So my question is : which sites are known to be the most pro-active against bots ? Is it just Pokerstars doing this ? (and if so, they will tend to get my business)